In a batch type heat processing apparatus, a heat processing method using a dummy wafer is used in order to maintain high in-plane uniformity and inter-plane uniformity and high reproducibility of heat processing even when an empty region where target substrates for processing are not loaded exists.
In the method, when there is an empty region, product wafers are maintained in a position biased upstream of a flow of processing gas while a dummy wafer is held in a position of directly downstream of the product wafer group. As a result, high in-plane and inter-plane uniformity may be obtained and high reproducibility of heat processing can be maintained even when there is an empty region.
Recently, with miniaturization of transistors, there is a need to more precisely control the amount of impurities being introduced. In the past, a minute variation of the amount of impurities being introduced has not presented a problem until now. However, if transistors were to be further miniaturized, even a slight variation of the amount of impurities being introduced may present a problem, for example, in a deviation of work function or a deviation of resistance value.
To use a dummy of a substrate to be processed, a so-called dummy wafer in a batch type heat processing apparatus is one of several effective methods for more precisely controlling the amount of introduced impurities. Through the use of a dummy wafer, it is possible to improve the in-plane uniformity of the amount of introduced impurities and the inter-plane uniformity between a plurality of product wafers of batch processing units, when compared with when the dummy wafer is not used.
However, in a case where impurities such as boron are vapor-diffused while the dummy wafer is used in the batch type heat processing apparatus, it was confirmed that although being very small, the amount of boron introduced into a product wafer was increased whenever the vapor diffusion was repeated. Accordingly, the use of a dummy wafer presented a new problem that it is difficult to obtain stability of the amount of introduced impurities between batch processing units.